Multiphoton transitions between energy levels in a phase-biased Cooper-pair box

TL;DR

This paper explores the dynamic behavior of a phase-biased charge qubit, demonstrating multiphoton excitation processes and their effects on the qubit's inductance through combined theoretical and experimental analysis.

Contribution

It provides a detailed investigation of multiphoton transitions in a phase-biased Cooper-pair box, with quantitative agreement between theory and experiment.

Findings

Detection of one-, two-, and three-photon excitation processes

Alteration of qubit inductance under microwave irradiation

Quantitative match between theoretical predictions and experimental data

Abstract

We investigated both theoretically and experimentally dynamic features of a phase-biased charge qubit consisting of a single-Cooper-pair transistor closed by a superconducting loop. The effective inductance of the qubit was probed by a high-quality tank circuit. In the presence of a microwave power, with a frequency of the order of the qubit energy level separation, an alteration of the qubit inductance was observed. We demonstrate that this effect is caused by the redistribution of the qubit level population. The excitation of the qubit by one-, two-, and three-photon processes was detected. Quantitative agreement between theory and experimental data was found.